The objectives of this study are a) to determine the metabolic fate of circulating cortisol (F) in mature female baboons and compare it with that in humans; b) to describe the changes in F metabolism induced by pregnancy in the baboon, and c) to compare the metabolism of F by newborn and postpartum baboons and determine the cortisol binding capacity of serum from maternal and fetal baboons during the course of pregnancy. This study is part of a continuing effort to evaluate and use the baboon as a model for studies of human pregnancy. Metabolic studies require administration of C14-cortisol to baboons (Papio papio) and isolation of radiolabelled metabolites from the urine. The cortisol binding capacity of serum is estimated from the mass of cortisol bound by serum stripped of endogenous steroids.